1. Field of the Invention
This invention relates to room temperature curable organopolysiloxane compositions. More precisely, this invention relates to room temperature curable organopolysiloxane compositions which are suitable as sealing materials in civil engineering and construction and to methods for producing these compositions. The compositions exhibit storage stability when protected from moisture, but they are cured when exposed to moisture to form highly elastic/low modulus silicone rubbers.
2. Description of the Prior Art
Information is available about room temperature curable organopolysiloxane compositions comprised of an organopolysiloxane containing silicon-bonded hydroxyl groups at the end of the molecular chains and knowledge exists of organosilicone compounds containing at least three silicon-bonded groups per molecule which are hydrolyzable by water e.g., oxime groups, alkoxy groups, amino groups, vinyloxy groups, amide groups, imide groups, lactam groups or aminoxy groups and which serve as crosslinking agents.
However, it was difficult to obtain highly elastic/low modulus silicone rubbers from these organopolysiloxane compositions. That is, high molecular weight substances must be used as the hydroxyl terminated organopolysiloxane in order to obtain silicone rubbers possessing these characteristics. If a high molecular weight substance is used, it creates difficulties in handling due to the high viscosity, causing inefficiency in the manufacturing process and operational problems in extruding products. Thus, there is a limitation on the magnitude of the molecular weight which may be used. Therefore, the physical properties, such as high elongation and low modulus, of silicone rubbers are also limited.
In an attempt to overcome these drawbacks, various room temperature curable organopolysiloxane compositions have been proposed which are comprised of a relatively low viscosity, hydroxyl terminated organopolysiloxane and a bifunctional organosilicone compound as the chain extender. For example, a method for producing highly elastic/low modulus silicone rubbers was disclosed in U.S. Pat. No. 3,341,486 by Robert A. Murphy, issued Sept. 12, 1967. In this patent, a mixture of an organosilicone compound possessing two silicon-bonded aminoxy groups per molecule and serving as the chain extender and an organosilicone compound possessing at least three silicon-bonded aminoxy groups per molecule and serving as the crosslinking agent are added to a hydroxyl terminated organopolysiloxane in order to carry out both the chain extending and crosslinking reactions simultaneously in the presence of water.
However, these room temperature curable organopolysiloxane compositions containing aminoxy groups have the following drawbacks. The aminoxy groups are relatively sensitive to moisture. In addition, the basicity is high and, specifically, chain cleavage of the polydiorganosiloxane occurs in a single package. Because of these drawbacks, the storage stability is insufficient even under closed conditions. The compositions are particularly unstable in the presence of a catalyst.
Other compositions which cure at room temperature to low modulus silicone elastomers are known. For example, Clark et al. in U.S. Pat. No. 3,766,127, issued Oct. 16, 1973, describe obtaining a low modulus silicone rubber from a composition prepared by mixing 100 parts by weight of a hydroxyl endblocked polydiorganosiloxane, 3.5 to 8 parts by weight of a silane of the formula ##STR1## where R" is methyl or vinyl and R'" is methyl, ethyl or phenyl and 0.3 to 4.2 parts by weight of a silane of the formula ##STR2## Brady et al. in U.S. Pat. No. 3,766,128, issued Oct. 16, 1973, describe obtaining low modulus silicone rubber from a composition prepared by mixing 100 parts of a hydroxyl endblocked polydiorganosiloxane, 2 to 7.5 parts by weight of methylvinyldi-(N-methylacetamido)silane, and 0.5 to 4 parts by weight of an aminosilane of the formula EQU R.sup.IV Si(N R.sup.V R.sup.VI)3
where R.sup.IV is alkyl, phenyl, or vinyl, R.sup.V is hydrogen or alkyl and R.sup.VI is alkyl or phenyl. Toporcer et al. in U.S. Pat. No. 3,817,909, issued June 18, 1974, describe obtaining a low modulus silicone rubber from a composition obtained by mixing 100 parts of a hydroxyl endblocked polydiorganosiloxane, 2 to 20 parts by weight of a silane of the formula ##STR3## where R.sup.VII is methyl, vinyl, or phenyl and R'" is defined above, and 0.25 to 7 parts by weight of an aminoxysilicon compound having 3 to 10 aminoxy groups per molecule.